1. Field of the Invention
The present invention relates to an improved process for the recovery of acetic acid from very dilute aqueous solutions of same. By the term "dilute aqueous solutions" in the present specification and claims is meant aqueous solutions with an acid content of 0.5 to 3% by weight.
2. Description of the Prior Art
The known techniques for the recovery of acetic acid from its aqueous solutions generally consist of continuously extracting same, in the liquid phase, by means of a solvent selected both for its high coefficient of extraction of the subject acid and for its selectivity, namely, selected for the ratio of enrichment with acid relative to water content of the said solvent, and which is achievable with such solvent.
According to these known techniques, the extract layer, in which the concentration of the acid relative to water is generally greater than its concentration in the mixture to be treated, is subsequently continuously distilled to initially separate the acid in anhydrous state, and which no longer contains any solvent, and secondly and simultaneously, to separate by hetero-azeotropic distillation the hydrated and deacidified solvent and the water. The hydrated solvent is recycled to the extraction stage. The aqueous solution, from which the acid has been removed, is treated in an extraction column to recover dissolved solvent.
The solvent can be a single organic compound or a mixture of organic compounds.
For a given solvent, the economics of the separation stage, which stage reflects the relative amounts of acetic acid and water contained in the organic layer, depend, all other conditions being equal, on the concentration of acetic acid in the initial aqueous solution to be treated. As a result, the amount of heat energy to be provided in order to isolate the acetic acid from the acidic organic solvent layer is the higher, the lower being the initial concentration of the aqueous acetic acid solution which is to be extracted.
If the acid content is of the order of 1 to 3%, the cost of the heat energy and, correspondingly, the magnitude of the investment required becomes prohibitive, even to the point of exceeding the intrinsic value of the anhydrous acid thus obtained.